The present invention relates to directional drilling with coiled tubing. More particularly, bottom hole assembly apparatus including an orienting tool driven through a clutch and mud motor, a bent housing and a mud motor driving a drill bit.
In conventional jointed tubing directional drilling, a drilling assembly, bent housing and motor are located at the downhole end of a rotary drill string. Additionally, a measurements-while-drilling (MWD) tool is used to signal drilling orientation and direction. Directional drilling is accomplished with an alternating combination of two drilling operations; a relatively short duration of steering or sliding; and a longer period of rotating. The result is a relatively continuous and curved borehole from the kick off point to the end of the curve.
More specifically, during the sliding operation, the drill string is slowly rotated to orient the bent housing in the desired direction. The mud motor is then energized so as to drill a curved path in the oriented direction. The non-rotating drill string slides along the borehole as the mud motor drills the curved path. The sliding phase is necessary for adjusting or setting the direction of the borehole path, however this phase is somewhat inefficient due to factors including: the indirect angular path, the drag of the sliding drill string, and the sole use of the mud motor. Once the desired borehole inclination is established, a rotating operation commences which uses a combination of simultaneously rotating the mud motor/drill bit and the drill string (which continuously rotates the bent housing) and which favorably results in both a higher rate of penetration (ROP) and a substantially linear path.
In conventional coiled tubing directional drilling, the coiled tubing cannot be rotated and thus is unable to implement the higher efficiency rotating operation available with jointed tubing drilling. A sliding-only operation is achieved using a bottom hole assembly (BHA) mounted at the downhole end of the coiled tubing. The BHA comprises a MWD tool, a mud motor, an orientor, a bent housing and a drill bit. The flow of mud through the coiled tubing and mud motor rotates the drill bit.
In coiled tubing directional drilling, the driller sets the build-up rate, which is a measure of increasing borehole inclination from vertical, by setting the angle of the bent housing at the surface. The angle of the bent housing, typically xc2xd to 3xc2x0 from the axis of the tubing, sets the drill bit toolface angle. The bent housing angles are typically invariant, and once downhole, the angle is generally fixed until such time as the string is tripped-out and the angle of bent housing is changed at the surface. The orientor can be incrementally rotated while downhole to redirect the bent housing. The orientor is actuated remotely through a cycling of the pressure of the mud in the coiled tubing. Accordingly, the conventional coiled tubing directional drilling mode available to the applicant is a serpentine or tortuous path resulting from successive implementation of sliding operations; first drilling an arcuate path one direction (build) and, when so indicated by the MWD, an arcuate path in an opposing (drop) direction.
In patent application WO 97/16622 to Rigden et al., a system is disclosed which uses an upper motor which, through a pivot, rotatably drives a section of drill pipe having a bend sub and second mud motor and drill bit. The upper motor is supported from the coiled tubing. A coupling device is positioned between the upper motor and the lower drill pipe. Coupled, the upper motor rotates the lower drill pipe, bent housing and drill head resulting in straight drilling. Uncoupled, the drill head drills in the last orientation. The preferred coupling device is a flow rate controlled device positioned uphole from the upper motor. A fixed sleeve has a first port exposed to the drilling mud directed to the drill head. A second outer sleeve has a piston exposed to the mud and a resisting spring. At low mud flow rates, the force of the piston cannot over come the spring and 100% of the mud flows to the drill head for directional drilling. At higher mud rates, the force of the piston overcomes the spring and the outer sleeve slides over the first sleeve, aligning a second port in the second sleeve with the port in the first sleeve. A portion of the mud flow is redirected into an annular passage for driving the upper motor. The speed of rotation of the drill pipe is wholly controlled by mud flow, the response of the spring constant, and the variable sleeve movement. When directional drilling, reactive torque in the drill pipe is presumably fed back in to the upper motor.
In WO 93/10326 to Hallundbaek, referred to in WO 97/16622, a system using reactive torque is utilized. No upper motor is employed. Drill bit and toolface interaction results in reactive torque being transmitted along the bent sub. A pivot between the bent sub and the coiled tubing permits contra-rotation. The speed of rotation is controlled using a brake comprising a complex arrangement of a plurality of hydraulic pump devices stacked in the annulus of the swivel. Each hydraulic pump assembly comprises a radial array of small hydraulic pistons and cylinders, the pistons normally driving a circumferential cam in pump mode. In reverse, relative rotation drives the pistons and a hydraulic throttle valve restricts the hydraulic flow, braking rotation therebetween. A mud flow restriction is provided through the swivel for actuating a lock across the swivel. At higher flow rates, increased pressure drop causes the swivel to lock and enable a change of drill pipe direction. As long as flow rates are high the swivel is locked and the bent sub rotates. When the flow reduces, the lock disengages and contra-rotation and straight drilling resumes.
To date, prior art coiled tubing directional drilling apparatus and methodology are associated with certain disadvantages. In the more conventional single motor case, operations are restricted to a series of sliding-only operations, and the disadvantages associated with the resulting and typically tortuous borehole path include: reduced rate-of-penetration (ROP); toolface angle drift as a result of the reactive torque; increased borehole length; reduced weight-on-bit (WOB), further reductions in ROP, and increased likelihood of a stuck tubing string, caused by increased frictional drag. In known dual motor implementations, the variable coupling between upper motor and drill head is dependent upon maintaining specified mud flow rates. Further, the means for alternating between straight and sliding operations are either variably flow dependent or are mechanically complex, which may result in uncertain drill pipe rotation rates.
The present invention is an improved directional drilling apparatus and method for use with coiled tubing. The principle implements a BHA connected to the coiled tubing and comprises a rotary bit and a bent housing which can be rotated substantially continuously, and at will, for enabling both sliding and rotating operations, heretofore not available with coiled tubing.
In a broad aspect, a method is provided for directional drilling of non-tortuous boreholes with a coiled tubing BHA having a bent housing and a rotary drill bit, the bent housing being alternately coupled using a clutch to the coiled tubing for alternately implementing sliding operation and then rotating or straight operation by rotating the drill bit while simultaneously rotating the bent housing. The coupling comprises operation of a clutch between first and second positions, the first position for rotation of the bent housing under direct driven or reactive torque contra-rotation for straight drilling, and the second position for locking the rotation of the bent housing so as to prevent reactive rotation during sliding. Mud flow is cycled to shift the clutch between first and second positions. Subsequently, mud flow is cycled again to shift the clutch between the second and first positions. One shifted between positions, variable flow rates thereafter can be used to vary drilling characteristics in either the first or second positions without affecting the sliding or straight drilling operations. Preferably, in straight drilling, a flowmeter is also employed for providing feedback enabling monitoring of the bent housing rotation rate during straight drilling.
In a broad apparatus aspect for implementing the novel method, the apparatus comprises: a rotary connection between the coiled tubing and the bent housing. A fluid pressure-actuated clutch alternatively permits the bent housing to rotate or be locked to the coiled tubing. In one embodiment, a first downhole motor rotates the drill bit and a second downhole motor rotates the bent housing through the clutch. In another embodiment, the first downhole motor is not required, a high reduction speed reducer being positioned between the coiled tubing and bent housing so as to permit the bent housing to contra-rotate slowly under reactive torque developed by the rotating drilling bit. Preferably, an energy dissipating device or flowmeter provides control of the rate of contra-rotation.